The present application relates generally to the field of mechanical resonance based sensors for use in sensing the presence of, for example, environmental contaminants.
The technique of mechanical resonance based detection and sensing at micro/nano scales has been shown to be capable of achieving resolutions equivalent to that of a proton mass. Such sensors rely on the frequency shift and/or amplitude change of a very narrow-band resonator. A measurable response change may be obtained by overcoming damping effects, which are detrimental in this context. The primary aim in the design of resonator-based sensing has previously been to minimize all dissipative effects.
Dissipation may result both from viscous friction with the fluid media that interacts with the sensor and also from internal losses of the material, the former being typically dominant in mechanical resonator systems. Minimization of viscous damping has been achieved by operating the system in high vacuum, but the inevitable presence of air in the system prevents the complete elimination of viscous damping. This viscous friction becomes more of a concern with the miniaturization of the systems to the sub-micron and nanoscales, which are intended to attain higher sensitivities and resolution. The wide practical application of such systems with a consistent high vacuum and low temperatures is uneconomical and impractical.
The study of the dissipation in micro-cantilevers for sensing purposes has also been considered. The dissipation in the cantilever is influenced by changes in the media, such as addition of other gases and the attachment of microorganisms (e.g., Bacillus anthracis) to the cantilevers. These studies were based on measuring the dissipation and corresponding frequency shift exhibited by a single resonator. For such a single-resonator system, the relative change of dissipation and subsequent change of frequency is proportional to the relative change of kinematic viscosity. The use of dissipation itself in such systems presents a challenge as it reduces the quality factor of the resonator, and limits the ability to measure the corresponding frequency shift. For example, a relative change in viscosity by 1% will lead to a corresponding change in dissipation of about 1% as well. In addition, using this method, it is difficult to obtain a good selectivity of the device.
It would be advantageous to produce an improved sensor incorporating a single mechanical resonator. The improved sensor provides increased sensitivity at reduced cost. These and other advantages will be apparent to those reviewing the present disclosure.